As products that include optical components become smaller and smaller, there is increased demand for smaller optical devices such as diffractive optics. One of the simplest forms of diffractive optics is amplitude gratings, which are simply based on the application of Huygens's principle to a light beam. FIG. 1 illustrates a two dimensional Fresnel zone plate based on amplitude grating 102, which is formed on substrate 100. Substrate 100 is substantially transmissive to incident light 104, which is show in FIG. 1 as being monochromatic with a wavelength of λ, and the concentric annular regions of amplitude grating 102 are substantially opaque to incident light 104. The concentric annular regions, or rings, of amplitude grating 102 are sized and arranged in a predetermined pattern on the substrate surface to produce a desired diffraction pattern, which focuses a portion of incident light 104 to focal spot 106. Thus, the two dimensional Fresnel zone plate may act as a diffractive lens. Although diffractive lenses of this sort have relatively low efficiency and large chromatic aberrations, they are easy to produce and may be very compact, particularly when compared to refractive lenses.